In modern deep well structures, elongate, substantially vertical holes or bores are drilled down into the earth and into structure or zones in the earth in which the oil, gas, water or steam to be produced by the wells is contained. It is common and well-known practice to support the earth defining the drilled bores of such wells with elongate strings of larger diameter casing pipe which often terminate above the production zones of the wells and to extend elongate strings of liner pipe, smaller in diameter than the casing pipe, down into the well bores below the lower ends of the casing pipes and into the production zones. Such liners are commonly lowered down through the casing pipes by elongate setting strings of drill pipe or the like and the upper end portions of the liners are connected to and with the lower end portions of the casings by means of liner hangers at the upper ends of the liners, whereby the liners are carried by and depend from the casings when released by the setting strings.
Liner hangers are tools which characteristically include elongate, vertically extending tubular bodies substantially equal in inner side diameter with the inside diameter of their related liners and which are slightly smaller in outside diameter than the inside diameter of the casings in which they are related. Accordingly, while the hanger bodies may have wall thicknesses which are greater than the wall thickness of their related liners and casings, their wall thickness and strength is quite limited.
The lower ends of the liner hanger bodies are commonly threadedly coupled with the upper ends of their related liners, while the upper ends thereof are commonly releasably coupled with the lower ends of their related setting strings by means of setting tools on those strings.
The bodies of one type or class of liner hangers are provided with upwardly and outwardly divergent, radially and downwardly disposed cone portions intermediate their ends and a plurality of circumferentially spaced wedges or slips which are less in vertical extent that the cone portions arranged about and carried by said cone portions. The slips are shiftable vertically from lower unactuated positions to upper actuated positions relative to the cone portions of their related hanger bodies and have inside surfaces which slidably engage said cone portions and have outside surfaces which occur at or inward of the exterior surfaces of the hanger bodies when the slips are in their unactuated positions and which engage the inside surfaces of their related casings when said slips are in their actuated positions. When the slips are in their actuated positions, they establish tight wedging engagement with and between their related casings and hanger bodies to effectively anchor or set the hangers with their liners depdnding therefrom, within their related casings. Movement of the slips in such tools, from their unactuated to their actuated positions, is effected by several different kinds and forms of setting tools and/or setting means which setting tools or means are, in most instances, operatively related to some releasable coupling means which is provided to couple the upper ends of the hanger bodies with their related setting strings provided to lower the liners and hangers into the wells.
While the above type or class of liner hanger has proven to be satisfactory to carry and support moderately heavy liners, the cone portions established in the liner hanger bodies so weaken the bodies that when they are subjected to the weight of liners, the weight of which is greater than moderate, they tend to deform or collapse inwardly when the slips are actuated and set in related casings. When the bodies of hangers deform or collapse in the manner suggested, they are rendered inoperative, ineffective to set and/or support the related liners.
In those instances where liners of greater than moderate or average weight are to be set in wells, use of another and special type or class of liner hanger is often resorted to. This special class of liner hanger differs from the previously described type or class of liner hanger in that the hanger bodies are provided with circumferentially spaced longitudinally extending slip receiving recesses with upwardly and outwardly inclined, radially outwardly and downwardly disposed slip engaging ramp surfaces, rather than with the aforementioned slip supporting cone portions. The provision of the noted slip recesses requires the removal of notably less material from the liner hanger bodies than is required to establish cone portions and therefore results in liner hanger bodies which are notably stronger and capable of supporting greater weight before the bodies will deform or collapse under radially inwardly disposed forces imposed upon them by the slips.
While the last noted special class of liner hangers are, as a general rule, stronger and capable of carrying heavier loads than the first noted class of liner hangers, they include features which limit their strength and which render them incapable of safely and effectively handling the ever-increasing weight of the "heavy" liner hangers now being used in wells.
In the above noted special class of liner hanger, the slips are characteristically normally yieldingly urged upwardly from unactuated or lower positions to actuated or upper positions by spring means carried by the hanger bodies below the recesses therein and engaging the lower ends of the slips. The slips are releasably held down in their unactuated position and against the resistance of the spring means by elongate vertical fingers on setting tools releasably coupled with the upper ends of the bodies. The fingers normally engage the upper ends of the slips to hold them down in their related recesses and against the force of the spring means. Since the noted fingers cannot be let to become obstructive and must occur inward of the exterior surfaces of their related hanger bodies, the hanger bodies are provided with elongate, vertically and radially outwardly opening grooves, between the slip recesses and the tops of the bodies to accommodate and protect the fingers. The noted grooves must extend down into the slip recesses to or below that line or point where the upper ends of the slips occur when the slips are in their unactuated or down position. Accordingly, the noted grooves necessarily extend through the upper portions of the inclined slip supporting ramp surfaces of the slip recesses and into and through the portions of the hanger bodies occurring directly inward of the slips, when the slips are in their actuated positions. It is those portions of the hanger bodies which must withstand the principal radially inwardly directly forces exerted onto and through the hanger bodies.
In practice, the vertical extent of the slips is equal to about one-half the vertical travel of the slips between their unactuated and actuated positions, the width of the fingers provided to hold the slips down is generally about one-quarter the width of the slips and the radial extent or depth of the grooves for the fingers is at least one-half the maximum depth of the recesses and/or one-half the maximum radial thickness of the slips. Accordingly, the portions of the grooves extending into the recesses generally leave about one-quarter of the central portions of the slips unsupported when the slips are in their upper actuated positions of the recesses.
As a result of the above, the noted grooves materially weaken the primary load-carrying portions of the hanger bodies and, by their very nature, establish break or bend lines in the hanger bodies, inward of and between opposite side portions of the slips which transmit the radially inwardly directed forces onto the bodies. Further, the extensions of the finger grooves in the hanger bodies above the slip recesses extend the break or bend lines in the bodies and so weaken and reduce the strength of the bodies above the recesses that little resistance to deformation of the bodies, inward of the slips, is afforded by the portions of the bodies above the slips.
In accordance with the above, it is apparent that the special form or class of liner hanger noted above have inherent weaknesses.
In addition to the foregoing, the longitudinal extent of the slip-engaging fingers is limtied to that length which imparts into the fingers sufficient rigidity and strength so that the fingers will not flex or bend out of engagement in their related grooves and cannot be washed, bent or dragged from engagement in said grooves by fluids and obstructions likely to be encountered in well structures. This limitation imposed upon the slip fingers works to limit the longitudinal extent of the portions of the hanger bodies which occur above the slips and with which the setting tools for the hangers are commonly engaged. As a result of the foregoing, it is not infrequent that the slips in such liner hangers are so closely related to the setting tools that if the hanger bodies yield inwardly, as and when the slips are set, proportions of the bodies, above the slips and within which the setting tools are related, yield or collapse to such an extent that the setting tools bind or are otherwise rendered inoperative. When the above occurs, costly fishing operations must be undertaken to retrive the setting tools, liner hangers and liners from within the wells. To overcome the above, and to enable the longitudinal or vertical spacing of parts and portions of the liner hangers and the setting tools to be increased, the length of the upper portions of the hanger bodies have been increased and the slips have been provided with upwardly projecting fingers which extend through the lower portions of related grooves in the hanger bodies to releasably engage the lower ends of the fingers of the setting tools engaged in the upper ends of the grooves. This practice has allowed the length of said upper portions of the hanger bodies, occurring above the slips, to be substantially doubled and has proven to be an improvement, but it is not a sufficient improvment to enable those liner hangers to effectively support those heavy loads which are now being encountered, without a likelihood of failure.
In practice, the slip engaging fingers are, at best, sufficiently long and fragile so that following actuation of the setting tools and disengagement of the fingers from their related grooves, the fingers are frequently mutilated or damaged to such an extent that they must be replaced before the setting tool can be used again. The difficulty and the cost of replacing those fingers is substantial.
In practice, liner hangers are provided with one or a plurality of longitudinally spaced sets of slips. Each set of slips most commonly includes three or four circumferentially spaced slips with related recesses, grooves and fingers. The space between adjacent recesses and/or slips of each set of slips is generally insufficient to accommodate finger-accommodating grooves for a next lower set of slips. Accordingly, where more than one set of slips is provided, it is necessary and common practice to arrange the slips of each lower set of slips so that the lower edges of slips of the next above set of slips engage and normally hold the lower slips down. Accordingly, grooves and fingers need only be provided for the uppermost set of slips. The great disadvantage of the above practice resides in the fact that substantial and most advantageous longitudinal spacing of sets of slips is prevented and excessive weakening of the hanger bodies is brought about by the close relationship of the vertically related slip recesses.
In instances where the circumferential spacing of the slips of an upper set of slips has been increased to accomodate the establishment of finger grooves for a next lower set of slips, the additional and longer grooves for the lower set of slips greatly weakens the hanger bodies where maximum strength should be maintained and the fingers for the lower sets of slips must be made so long and fragile that they are subject to being displaced before the hangers are in place and ready to be set.
In those situations where the weight of liners could be set is greater than the weight ordinary or commercial available liner hangers can support are encountered, well drillers have resorted to the purchase and use of custom made liner hangers which, to the best of my knowledge and belief, are not materially different in design and construction from ordinary, commercially available liner hangers, but are made of costly and/or exotic materials under rigid quality control standards. The cost of one such custom made liner hanger is understood and believed to be approximately $40,000.00. That hanger was used in a well structure where an ordinary commercially available liner hanger costing approximately $5,000.00 would have been used, if such an ordinary hanger could be relied upon to carry the anticipated weight of the liner being handled. That liner is understood to have been a 121/2" liner, 6,000 ft. long and weighing about 284,000 lbs. The liner hanger, in this case, was subjected to a maximum load of about 350,000 lbs. when the slips were being set and the weight of the setting string was imposed upon the hanger to set the slips in tight wedging engagement between the hanger body and casing.
In the foregoing, reference to those weights of liners which are of moderate to heavy weight and reference to the strength and weight carrying capacity of various liner hangers necessarily refers to such factors in a general sense and is intended to point to certain of those factors which adversely affect the utility of most commonly used and commercially available liner hangers provided by the prior art. It is recognized that in certain instances and/or under certain circumstances, exceptions to the foregoing might be found.